khó quá 

\(a.\frac{-5}{9}+\frac{5}{9}:A=\left(-\frac{5}{9}+\frac{5}{9}\right):A=0:A=0\)

\(b.\frac{7}{25}.\frac{11}{13}-\frac{7}{25}.\frac{2}{13}-\frac{8}{25}=\frac{7}{25}.\left(\frac{11}{13}-\frac{2}{13}\right)-\frac{8}{25}=\frac{7}{25}.\frac{9}{13}-\frac{8}{25}=\frac{63}{325}-\frac{8}{25}=\frac{-41}{325}\)

C.Thua

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a)\(\frac{-5}{13}+\left(\frac{3}{5}+\frac{3}{13}-\frac{4}{10}\right)=\frac{-5}{13}-\frac{3}{5}-\frac{3}{13}+\frac{4}{10}=\left(\frac{-5}{13}-\frac{3}{13}\right)+\frac{4}{10}-\frac{3}{5}=\frac{-5-3}{13}+\left(\frac{4}{10}-\frac{6}{10}\right)=\frac{-8}{13}+\frac{-2}{10}=\frac{-80}{130}+\frac{-26}{130}=\frac{-106}{130}=\frac{-53}{65}\)

tại sao bạn ra \(\frac{-5}{13}\)

a) \(\frac{5}{9}:\frac{13}{7}+\frac{5}{9}:\frac{13}{9}-1\frac{2}{3}\\ =\frac{5}{9}\cdot\frac{7}{13}+\frac{5}{9}\cdot\frac{9}{13}-\frac{5}{3}\\ =\frac{5}{9}\left(\frac{7}{13}+\frac{9}{13}\right)-\frac{5}{3}\\ =\frac{5}{9}\cdot\frac{16}{13}-\frac{5}{3}\\ =\frac{80}{117}-\frac{5}{3}\\ =\frac{80}{117}-\frac{195}{117}=\frac{-115}{117}\)

b) \(\left(15-6\frac{13}{18}\right):11\frac{1}{27}-2\frac{1}{8}:1\frac{11}{40}\\ =\left(\frac{270}{18}-\frac{121}{18}\right):\frac{298}{27}-\frac{17}{8}:\frac{51}{40}\\ =\frac{149}{18}\cdot\frac{27}{298}-\frac{17}{8}\cdot\frac{40}{51}\\ =\frac{3}{4}-\frac{5}{3}\\ =\frac{9}{12}-\frac{20}{12}=\frac{-11}{12}\)

1.

a) \(\dfrac{5}{18}+\dfrac{4}{7}+\dfrac{13}{18}+\dfrac{3}{7}\)

\(=\left(\dfrac{5}{18}+\dfrac{13}{18}\right)+\left(\dfrac{4}{7}+\dfrac{3}{7}\right)\)

\(=1+1=2\)

b) \(\dfrac{4}{9}.\dfrac{5}{19}.\dfrac{9}{4}\)

\(=\left(\dfrac{4}{9}.\dfrac{9}{4}\right).\dfrac{5}{19}\)

\(=1.\dfrac{5}{19}=\dfrac{5}{19}\)

tik mik nha!!!

2) \(\dfrac{4}{9}.\dfrac{5}{19}.\dfrac{9}{4} =(\dfrac{4}{9}.\dfrac{9}{4}).\dfrac{5}{19} =1.\dfrac{5}{19} =\dfrac{5}{19}\)

Câu b) đề sai phải ko bạn

bài 1b)

\(8\frac{1}{14}-6\frac37\)

C1:\(\frac{113}{14}-\frac{45}{7}\) =\(\frac{113}{14}-\frac{90}{14}=\frac{23}{14}\)

C2:\(8\frac{1}{14}-6\frac37=\left(8-6\right)+\left(\frac{1}{14}-\frac37\right)=2+\left(\frac{1}{14}-\frac{6}{14}\right)\)

\(=2+\frac{-5}{14}=\frac{28}{14}-\frac{5}{14}=\frac{23}{14}\)

bài 1 c)\(7-3\frac67\)

C1:\(\) \(7-3\frac67=7-\frac{27}{7}=\frac{49}{7}-\frac{27}{7}=\frac{22}{7}\)

C2:\(7-3\frac67=\left(7-3\right)-\frac67=4-\frac67=\frac{28}{7}-\frac67=\frac{22}{7}\)

a.

\(81^7-27^9-9^{13}=\left(3^4\right)^7-\left(3^3\right)^9-\left(3^2\right)^{13}=3^{28}-3^{27}-3^{26}=3^{22}\times\left(3^6-3^5-3^4\right)=3^{22}\times405\)

\(\Rightarrow81^7-27^9-9^{13}⋮405\)

b.

\(8^7-2^{18}=\left(2^3\right)^7-2^{18}=2^{21}-2^{18}=2^{17}\times\left(2^4-2\right)=2^{17}\times14\)

\(\Rightarrow8^7-2^{18}⋮14\)

\(81^7-27^9-9^{13}\)

\(=\left(3^4\right)^7-\left(3^3\right)^9-\left(3^2\right)^{13}\)

\(=3^{28}-3^{27}-3^{26}\)

\(=3^{26}\left(3^2-3-1\right)\)

\(=3^{26}.5\)

\(=3^{22}.3^4.5\)

\(=3^{22}.81.5\)

\(=405.3^{22}\)

\(\Rightarrow405.3^{26}⋮405\)

\(\Rightarrow81^7-27^9-9^{13}⋮405\)

a) \(\frac{-5}{9}+\frac{5}{9}:\left(1\frac{2}{3}-2\frac{1}{12}\right)\)

\(=\frac{-5}{9}+\frac{5}{9}:\left(\frac{5}{3}-\frac{25}{12}\right)\)

\(=\frac{-5}{9}+\frac{5}{9}:\frac{\left(-5\right)}{12}\)

\(=\frac{-5}{9}+\frac{5}{9}.\frac{12}{\left(-5\right)}\)

\(=\frac{-5}{9}.\left(1+\frac{12}{5}\right)\)

\(=\frac{-5}{9}.\frac{17}{5}\)

\(=\frac{-17}{9}\)

b) \(\frac{-7}{25}.\frac{11}{13}+\frac{-7}{25}.\frac{2}{13}-\frac{18}{25}\)

\(=\frac{-7}{25}.\left(\frac{11}{13}+\frac{2}{13}\right)-\frac{18}{25}\)

\(=\frac{-7}{25}-\frac{18}{25}\)

\(=-1\)

Chúc bn học tốt !!!

ổi câu a sao mk bấm mấy ra kq là 5/9